Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$235.90	7.352%	$253.2434	$253.24	$253.25	$253.20
Purchase #2	$87.60	3.335%	$90.5215	$90.52	$90.50	$90.50
Purchase #3	$126.52	4.422%	$132.1147	$132.11	$132.10	$132.10
Purchase #4	$26.33	7.287%	$28.2487	$28.25	$28.25	$28.20
Purchase #5	$174.69	9.373%	$191.0637	$191.06	$191.05	$191.10
Purchase #6	$111.56	7.485%	$119.9103	$119.91	$119.90	$119.90
Purchase #7	$102.30	11.793%	$114.3642	$114.36	$114.35	$114.40
7 purchase totals =	$864.90		$929.4665	$929.45	$929.40	$929.40